This invention relates to modular, multi-component connectors for high frequency data transmission, and particularly to connectors with compensation structures that balance cross-talk generated within the connectors.
Over the last decade, the deployment of new computer network architectures has increased the demand for improved data communication cables and connectors. Initially, conventional cables and connectors were used for voice transmission and for low speed data transmission in the range of a few megabits per second. However, because conventional data cables and connectors were inadequate for high speed, bit-error-free data transmission within current or proposed network architectures, new types of high speed data communication cables and connectors have been developed. Such new cables or connectors need to meet specific requirements such as low attenuation, acceptable return loss, low cross-talk and good EMC (ElectroMagnetic Compatibility) performance parameters. They also need to meet specific requirements with respect to impedance, delay, delay skew and balance.
Cables for transmitting high speed digital signals frequently make use of twisted pair technology, because twisted pairs eliminate some types of cross-talk and other noise. Near end cross-talk (NEXT) in one twisted pair arises from the neighboring xe2x80x9cdisturbingxe2x80x9d pairs inside the same cable. The cross-talk depends inversely on the square of the distance between the twisted pairs. In a twisted pair, each wire of the pair carries an information signal that is equal in amplitude and 180xc2x0 out of phase with the counter-part signal carried by the pair. That is, each twisted pair carries differential signals. Ideally, the proximity of the twisted pairs to each other causes cross-talk to affect both wires of the pair equally. Thus, this noise ideally appears in both wires of the twisted pair creating a common mode signal. Cross-talk coupled to the same pair within the same cable can be compensated by adaptive amplifier techniques that substantially reject common mode signals. However, differential noise coupled to a twisted pair cannot be compensated for.
Cross-talk is a measure of undesirable signal coupling from one signal-carrying medium to another. Several different measures of cross-talk have been developed to address concerns arising in different cables, communications systems and environments.
One useful measure of cross-talk is near-end cross-talk (NEXT). NEXT is a measure of the signal coupled between two media, e.g., two twisted pairs, within a cable. Signal is injected into one end of the first medium and the coupled signal is measured at the same end of the second medium. Another useful measure of cross-talk is far-end cross-talk (FEXT). Like NEXT, FEXT is a measure of the signal coupled between two media within a cable. A signal is injected into one end of the first medium and the coupled signal is measured at the other end of the second medium. Other measures of cross-talk, including cross-talk of other types exist. For example, so called alien cross-talk, which is coupling into a signal-carrying medium from outside of a cable, may also be of interest. However, issues pertaining to alien cross-talk are not addressed here.
A modular connector usually includes a modular plug that is mated with a jack that has a receptacle-type opening. The modular plug includes a set of contacts and a dielectric housing having a wire-receiving end, a contact-terminating end, and a passageway used for both communicating internally between the respective ends and receiving a plurality of conductors (or a set of rear terminals to be connected to the wires). Some plugs may include a passageway with two surfaces that separate selected pairs of the wires within the limits of the housing. A patch cord cable assembly includes a data transmission cable, typically with four twisted wire pairs, and two plugs. The four twisted pairs may be wrapped in a flat or a round insulating sheath. The bundle may optionally include a drain wire and a surrounding shield for use with a shielded plug. The goal is to minimize the EMC issues and EMI coupling to the outside environment as required by various regulations.
Modern data networks have the data transmission cables built into the walls of a building and terminated by a modular connector system to enable flexible use of space. Individual computers are connected to the network, using a patch cord cable assembly, by inserting a connector plug into a connector jack (or a receptacle).
Many prior art connector systems have been used to transmit low frequency data signals, and have exhibited no significant cross-talk problem between conductor wires of different twisted pairs at these low frequencies. However, when such connectors are used for transmission of high frequency data signals, cross-talk between different pairs increases dramatically. This problem is caused basically by the design of the prior art connectors, wherein the connector electrical paths are substantially parallel and in close proximity to each other, producing excessive cross-talk.
A number of popular modular, multi-conductor connectors have been used in telecommunication applications and data transmission applications. Such connectors include 4-conductor, 6-conductor and 8-conductor types, commonly referred to as RJ-22, RJ-11 and RJ-45 as well as other types of connectors of similar appearance. In the detailed description provided below, we will illustrate various novel concepts in connection with an 8-conductor connector system designed for high-frequency data transmission.
An 8-conductor connector system (e.g., an RJ-45 type connector system) includes a modular jack and a plug made from a plastic body surrounding and supporting eight signal-carrying elements. Specifically, an RJ-45 type plug has eight conductive elements located side-by-side. Each conductive element has a connecting portion, attached to a signal-carrying conductor, and a contact portion. An RJ-45 type jack also has eight conductive elements located side-by-side, and each conductive element has a connecting portion and a contact portion arranged as a cantilever spring. The eight conductive elements are connected to four twisted pairs in a standard arrangement. The entire connector may include a conductive shield.
As mentioned above, the modular connector system has the conductive elements placed straight in parallel and in close proximity to each other. The close proximity increases the parasitic capacitance between the contacts, and the straight parallel arrangement increases the mutual inductance between the contacts. These are a principle source of differential noise due to coupling. Specifically, the connector cross-talk occurs between the electric field of one contact and the field of an adjacent contact within the jack or the plug. The cross-talk coupling is inversely proportional to the distance between the interfering contacts. The signal emitted from one conductive element is capacitively or inductively coupled to another conductive element of another twisted pair. Since the other contact element is at a different distance from the emitting element, this creates differential coupling.
Standardization of equipment is in the interest of both manufacturers and end users. The performance requirements are specified in IEEE 802.3 for both the 10Base-T and the 100BaseTX standards, where the data is transmitted at 10 Mbps and 100 Mbps at frequencies above 10 MHz and 100 MHz, respectively. The transmission parameters, including attenuation, near-end cross-talk and return loss, are defined in EIA/TIA-568-A for unshielded twisted pair (UTP) connectors.
In an attempt to reach cross-manufacturer compatibility, EIA/TIA mandates a known coupling level (Terminated Open Cross-talk) in a Category 5 plug. The modular connector system may include counter-coupling or compensation structures designed to minimize the overall coupling inside the connector system. Counter-coupling, as used herein, relates to the generation of a signal within a pair of elements of the connector system that balances an interfering cross-talk signal. The effectiveness of this counter-coupling compensation is limited inasmuch as there is variability in the different plugs"" cross-talk coupling.
Frequently, it is possible to reduce the actual amount of coupling in a plug or in a jack of a connector system to improve the overall performance, but this is not desirable for reverse compatibility reasons. For example, the layman assembling a system would naturally expect that system built using a category 5 xe2x80x9clegacyxe2x80x9d plug connected to a superior performance jack would meet category 5 performance requirements. Similarly, the layman would expect that a superior plug connected to a category 5 jack would also meet the category 5 requirements.
Therefore, there is a need for an improved jack or an improved plug that can provide improved cross-talk performance for the entire connector system.
The invention is a high performance modular connector system that includes a plug and a jack both arranged for high frequency data transmission. The connector system includes several counter-coupling or compensation structures, each having a specific function in cross-talk reduction. The compensation structures are designed to offset and thus electrically balance frequency-dependent capacitive and inductive coupling. A compensation structure may itself cause additional capacitive or inductive coupling, which is then balanced or counter-coupled by another compensation structure. The overall design of the connector system minimizes cross-talk and thus reduces errors in data transmission due to parasitic effects.
According to one aspect, the connector system includes a compensation structure that includes several signal-carrying and compensation elements connected to connector contacts. The signal-carrying and compensation elements are disposed and arranged in a three-dimensional manner. That is, these elements are spaced both laterally and vertically along the length of the connector. The compensation elements are arranged to optimize the electrical transfer function of the connector system by balancing inductive or capacitive coupling introduced inside the connector system.
According to another aspect, the connector system includes a compensation structure that eliminates or minimizes random coupling caused by the random arrival angle of the individual conductors at the far end of each conductor. This compensation structure includes several channels for controlling location and relative orientation of the individual insulated conductors in a de-twisted region before the conductors are connected to connection terminals of a plug or a jack. This structure introduces a known amount of inductive and capacitive coupling between the insulated conductors.
According to yet another aspect, the connector system includes a compensation structure with a plurality of parallel conductive plates (or fins) electrically connected to connector elements (or contacts). The conductive plates are designed to provide capacitive coupling to reduce the coupling imbalances between conductors (or contacts) generated in the connector system. The capacitive coupling is relatively independent of the contacts forming the main signal path between the jack and the plug. Advantageously, these plates are located outside of the main signal parts. This location isolates the inductance due to the cantilever contacts from the compensating capacitance. Furthermore, the coupling structure is located relatively close to the contacts and thus there is only a minimal change in the phase of the signal due to propagation delay. That is, this capacitive coupling structure does not need to use flexible conductors within the jack or the plug; such conductors would introduce a larger phase delay.
The capacitive compensation structures also provide stable compensation signals relatively independent of the penetration and movement of the plug within the jack or external forces occurring when the two are mated. The capacitive coupling may also be relatively independent of the relative height of the contacts of the mated plug and jack.
The distance between the plates and the contact points should be minimal since mutual inductance between the plates and the contact points is undesirable. The relevance of this distance increases as the transmission frequency increases. Thus, the length of the cantilever contacts of the jack is minimized and is dictated mainly by mechanical and size consideration.
According to another aspect, a superior performance plug, described below, has a coupling level that matches the jack""s counter-coupling achieved by the capacitive compensation structure. Similarly, the jack""s counter-coupling is matched to the plug""s coupling level. In short, the present connector system achieves reverse compatibility, wherein the novel jack and plug xe2x80x9cemulatexe2x80x9d the xe2x80x9clegacyxe2x80x9d devices they replace. This novel compensation is provided with sufficient precision for counter-coupling to achieve reverse compatibility performance. Furthermore, the present connector system achieves higher performance goals when a higher performance plug is mated to a higher performance jack by providing the compensation structures for counter-coupling.
According to yet another aspect, the high frequency data connector includes a plug constructed for coupling in a mating arrangement with a jack both including a plurality of contacts arranged to provide conductive paths for carrying a high-frequency data signal, and a compensation structure providing compensation signals that balance a selected amount of cross-talk generated in the connector. The compensation structure is located near contact points forming the conductive paths between connector terminals of the jack and connector terminals of the plug. The compensation structure is conductively connected to at least some of the contacts and is located outside the conductive path carrying the high-frequency data signal. The preferred embodiment includes one or more of the following features: The compensation structure may be connected to contacts of the jack. The compensation structure may be connected to contacts of the plug. The compensation structure""s conductive connection does not include flexible conductors. The compensation structure is not located on a printed circuit board (or printed wiring board).
The jack may include a compensation insert including the contacts arranged to form cantilever springs mounted on the compensation insert. The compensation signals are substantially independent of a relative height between the cantilever springs. The compensation structure may include capacitive coupling elements.
The compensation structure is arranged to provide substantially constant compensation signals regardless of mechanical variability in mating between the jack and the plug.
The compensation structure may include capacitive balancers (or plates). The balancers may be located inside a housing of the jack and are conductively connected less than 0.4xe2x80x3 from the contact points, and preferably less than 0.1xe2x80x3 from the contact points, and more preferably less than 0.05xe2x80x3 from the contact points. The balancers may be located outside of a housing of the jack.
The above features provide exceptional advantages for the high frequency data transmission.